Stratigraphy and soils of late Quaternary terrace cover beds in the Wanganui and South Taranaki districts, North Island, New Zealand

Abstract

A late Quaternary stratigraphic model (last c.240 000 yrs.) for terrace cover beds and soils (including paleosols) for the Wanganui and south Taranaki districts is established. The identify of coastal terraces is tested using terrace elevations and cover bed stratigraphy; and a mean uplift rate of 0.4 to 0.9 m/k.yr. estimated. The thickness of the stratigraphic units is often small (c.50 cm) and the differing lithologies of loess, tephra, dune sands and alluvium, make important their study as lithostratigraphic units and as soils. An initial soil survey of the study area had established a wide range of soils (solum 1.0 to 1.5 m depth) but achieved little of an understanding of their relationships. Subsequent stratigraphic studies have established a time scale for Wanganui - south Taranaki cover deposits, have defined depositional environments for them, and have enabled comparative studies of these stratigraphic units with those of other parts of the North Island. Earlier assumptions made of the soil parent materials of modern soils are not well founded and this project amply demonstrates that a prior understanding of late Quaternary history is crucial to the effective interpretation of soil mapping units.